Layered materials with hierarchically structured materials have attracted a great amount of attention in recent years, as research have shown that the presence of hierarchical structures on materials can improve the performance of materials in various application areas such as optoelectronic, biomedical, and energy storage. By virtue of their highly porous structure and large specific surface area, these layered materials have excellent ion-exchange, molecular absorption, photoelectronicity and/or wettability contrast properties.
Functional materials such as silicon oxide (SiO2), titania (TiO2), tin oxide (SnO2), and manganese oxide (MnO2), and carbon (C) have been used in the synthesis of hierarchical structures such as column arrays, polyhedron-like particles, belt-branched, core-shell spheres and vesicles. Of these, titanium-based oxides, such as titania and titanate, are of particular interest because of their antimicrobial and self-cleaning properties.
Generally, formation of a hierarchical material is considered to be a self-assembly process, whereby building blocks, such as nanoparticles (0D), nanofibers or nanotubes (1D), and nanosheets (2D) self-assemble into a regularly arranged, higher level structure. The synthesis of the building blocks can take place via methods such as template assisted growth, solvothermal methods, and other template-free solution-based methods.
For example, current methods to manufacture titanate particles include the use of a hydrothermal method. However, this method suffers from drawbacks such as high processing pressures, heating of the processing solution (typically 100 to 200° C.), and a long processing time (ranging from 10 to 120 hours). These requirements can pose a limit on the process efficiency, thereby translating into high manufacturing costs during commercial production.
Other research in this area includes, for example, a molten-salt synthesis of a titania (TiO2) mixture at 825° C. for 3 hours, or a high-temperature oxidation of sodium hydroxide (NaOH) coated titanium (Ti) foils at 800° C. for 1.5 hours in the presence of oxygen (O2) and water (H2O) vapor. However, these processes are complicated and require an even higher processing temperature compared to that used in the hydrothermal method.
Therefore, there remains a need for an improved method to manufacture layered materials, in particular, layered metal oxide particles which can by themselves be used directly in various applications or be used as building blocks to form materials for application.